The present invention relates to an image fixing device for fixing an unfixed image, which is usable with an image forming apparatus such as a copying machine or a printer.
In a conventional transfer type electrophotographic copying machine, for example, a toner image is transferred from a photosensitive drum onto a transfer material, and the transfer the image is subjected to a heat pressing process using a fixing heat roller with the use of a temperature sensor in the form of a thermister or the like.
Generally, the heating means for the heat roller is in the form of a halogen heater.
Recently, in order to stably fix toner on the transfer material in a high speed color image forming apparatus, it is considered that both of the fixing rollers contain heaters which are temperature controlled. However, it becomes necessary that electric power supply to the halogen heaters which are used as the heating means for the heat rollers are significantly increased in the speed-up of the image forming apparatus. The halogen heater involves a property that upon the start of the electric power supply to the heating means, a large inrush current flows with the possible result of temporary voltage drop of the commercial voltage source.
Therefore, the measurement has been taken against the inrush current by a phase control or the like to reduce the electric energization angle of the TRIAC, the thyristor, the SSR or the like for controlling the heating means for a period of the ten or more cycles during which the inrush current influences the frequency of the commercial voltage source.
However, if a plurality of heating means are provided for a plurality of heat rollers, and the phase control is carried out sequentially, unwanted radio noise is produced upon the switching actions of the TRIAC, the thyristor, the SSR or the like.
Accordingly, it is a principal object of the present invention to provide an image fixing device in which the inrush current to the heater is reduced. It is another object of the present invention to provide an image fixing apparatus in which the generation of radio noise is controlled. According to an aspect of the present invention, there is provided an image fixing apparatus comprising a first rotatable member for being heated by a first heater; a first temperature detecting element for detecting a temperature of said first rotatable member; first control means for controlling electric energy supply through said first heater so as to maintain a detected temperature of said first temperature detecting element at a first target temperature; a second rotatable member for being heated by said second heater, said second rotatable member constituting a fixing nip with said first rotatable member; a second temperature detecting element for detecting a temperature of said second rotatable member; a second control means for controlling electric energy supply to said second heater so as to maintain the detected temperature of said second temperature detecting element at a second target temperature; and phase control means for controlling electric energy supply phase so as to avoid overlapping of a phase of an electric power supply to said first heater and a phase of an electric power supply to said second heater.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.